The microscopist : a manual of microscopy and compendium of the microscopic science : micro-minerology, micro-chemistry, biology, histology, and pathological histology / by J.H. Wythe.
- Joseph Henry Wythe
- Date:
- 1877
Licence: Public Domain Mark
Credit: The microscopist : a manual of microscopy and compendium of the microscopic science : micro-minerology, micro-chemistry, biology, histology, and pathological histology / by J.H. Wythe. Source: Wellcome Collection.
Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.
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![properly prepared transparent objects. A good half-inch objective should show the transverse markings between the longitudinal ribs on the scales of the Hi'p'parchia janira, butterfly (Plate I, Fig. 27), and the one-fourth or •one-fifth should exhibit markings like exclamation points on the smaller scales of Podura ylumbea (Plate I, Pig. 28) or Lepidocyrtis. High power objectives are chiefly used for the most delicate and refined investigations of structure, and are not so suitable for general work. It is with these glasses that angular aperture is so necessary to bring out striae, and dots, and other delicate structures, under oblique illumination. For these glasses, the best tests are the siliceous envelopes of diatoms, as the Pleurosigma angu- latum, Surirella gemma, Grammataphora subtilissima; or the wonderful plates of glass artificially^ ruled by M. ]^o- bert, and known as Nobert's test. The latter test is a series of lines in bands, the distance between the lines decreasing in each band, until their existence becomes a matter of faith rather than of sight, since no glass has ever revealed the most difiicult of them. The test plate has nineteen bands, and their lines are ruled at the following distances: Band 1, y,/„^,th of a Paris line (to an English inch as .088 to 1.000, or as 11 to 125). Band 2, f g'goth. Band 3, ^p'^^^th. Band 5, g^^^oth. Band 9, g^'goth. Band 13, ^g'^pth. Band 17, -go'^Qth. Band 19, ^^l^j^th. It is said that Ilartnack's immersion system ]^o. 10 and oblique light has resolved the lines in the 15th band, in which the distance of lines is about ^y Joo^^ ^^ ^^^ inch. The surface markings of minute diatoms are also ex- cessively fine. Those of Pleurosigma formosam. being from 20 to 32 in y ^j'^j^th of an inch ; of P. hippocampus and P. attenuatum, about 40 ; P. angulatum 46 to 52 ; Navicula rhomboides 60 to 111; and Atnphipleura pellucida 120 to 130. This latter has been variously estimated at 100,000](https://iiif.wellcomecollection.org/image/b21085225_0058.jp2/full/800%2C/0/default.jpg)
